Active stabilizer for marine vessels

ABSTRACT

Active tank ship&#39;&#39;s stabilizer devices are disclosed having symmetrically positioned variable active tanks operated in cooperation by a hydraulic actuator. The variable volume tanks are arranged to permit injection or ejection of ballast liquid in a system avoiding the unstabilizing effects of free liquid surfaces and the power consuming effects of high pressure-heads.

0 United States Patent 1 1 1 1 3,741,145 Braddon June 26, 1973 41 ACTIVE STABILIZER FOR MARINE 2,963,245 12/1960 11011011 244/93 VESSELS FOREIGN PATENTS OR APPLICATIONS Inventor: Frederick Braddon, Babylon, 324,340 1/1935 Italy 114/122 N.Y. 1,039,992 5/1953 France 114/125 [73] Assignee: Sperry Rand Corporation, New 9 York, NY Primary Exammer-Mdton Buchler Assistant Examiner-Stuart M. Goldstein 1 1 Ffled: 7 Attorney-S. C. Yeaton [21] Appl. No.: 91,774

[57] ABSTRACT [52] U.S. Cl. 114/125 Active tank P Stabilizer devices are disclosed [51] Int. Cl B631) 43/06 8 symmetrically Positioned variable active tanks P- [58] Field of Search 1 14/122, 125, 16 E; erated in cooperation y a hydraulic actuator- The vari- 244/93 able volume tanks are arranged to permit injection or ejection of ballast liquid in a system avoiding the unsta- [56] Ref c Ci bilizing effects of free liquid surfaces and the power UNITED STATES PATENTS consuming effects of high pressure-heads. 1,382,073 6/1921 Fort 114/16 E 1 Claim, 3 Drawing Figures FROM GAS COMPRESSOR 7 I4 V F I 2 7 I20 6 1 20 j 2 PATENIEflwnes ma 3.741. 1 45 satin or 2 FROM GAS COMPRESSOR INVENTOR. FREDERICK D. B/m000/v FIG. 2 BY ATTORNEY PAIENIEDJms man 3. 741; 145

SHEEIZG'Z FROM GAS COMPRESSOR INVENTOR FREDERICK D. B/PAODO/V BY Q ATTORNEY ACTIVE STABILIZER FOR MARINE VESSELS BACKGROUND OF THE INVENTION l. Field of the Invention The invention pertains to stabilization of craft and particularly concerns stabilization of marine vessels through the agency of improved active tank stabilizer apparatus.

2. Description of the Prior Art Prior art systems for stabilizing a marine vessel about its roll axis have included tank stabilizers which may be classified as belonging in passive, passive-controlled, and active categories. In passive and passive-controlled tank stabilizers, the stabilizing or ballast liquid is forced from one side of the ship to the other only by the ships rolling motion. The operation of the controlled-passive tank stabilizer is enhanced somewhat by the additional use of fast acting automatic valves that regulate the timing of roll-induced liquid flow. On the other hand, in the prior art active stabilizertank systems, the stabilizing liquid is moved from side to side in the vessel by a controlled high-capacity pump capable of forcing the liquid to move against large pressure heads.

The prior passive and passive-controlled tank stabilizers, though sometimes relatively inexpensive, are well known to have relatively low performance characteristics, i.e., they can only reduce roll, never eliminate it. Furthermore, performance is additionally degraded when the natural roll period of the vessel synchronizes with the period of encounter of the waves. Passive, or tuned, tanks are narrow-band devices'and should not be used where large variations in the natural frequency of the vessel are to be encountered.

Prior art tank stabilizer systems thus have resonance effects whose interrelations may severely limit ranges of usefulness of the stabilizer even, in some conditions,

tending to diminish the inherent stability of the vessel in which they are used and'to generate dangerous situations. Stabilizer action in the prior art active tank system is also not under positive control;thus, it cannot be adequately regulated to accommodate changing conditions which induce ship roll, such as sea state, the aspect of the waves, and varying conditions of ship loadmg.

Prior art active stabilizers employ ballast liquid storage permitting the liquid to .have large free surfaces whose transient motions may significantly impair the inherent stability of the vessel. Further, prior art active tank stabilizer systems do not avoid operation against large static pressure heads which impose severe capacity demands on the pumping mechanism. In some instances, the demand for pump capacity for transfer of ballast liquid against such large pressure heads is great enough to make costs prohibitive.

SUMMARY OF THE INVENTION The present invention concerns active tank ship's stabilizers having symmetrically disposed active variablevolume tanks whose effective volumes may be reciprocally controlled by a common actuator. The variable volume tanks are provided with means permitting injection or ejection of ballast liquid with respect to their interiors through operation of the actuator as determined by inertially derived control signals. The configuration including the active tank, means for varying the volume of the active tank, and means permitting ingress and egress of ballast liquid with respect to the tank is such that deficiencies of prior art tank stabilizer devices are overcome. No free liquid surfaces are permitted, so that undesired resonant and unstabilizing influences are minimized. The configuration also avoids power-consuming pressure heads and high velocity fluid transfer present in the prior art, thus significantly reducing initial and operating costs of the equipment and reducing the space within the vessel required for its installation.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an elevation view, partly in cross section, of one embodiment of the invention and is taken along the line 1-1 of FIG. 2.

FIG. 2 is a plan view, partly in cross section, of the embodiment of FIG. 1 and is taken along the line 22 of FIG. 1.

FIG. 3 is an elevation view, partly in cross section, of an alternative to the apparatus shown in FIGS. 1 and 2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIGS. 1 and 2, an embodiment of the invention is illustrated having common means for moving liquid ballast between. storage regions or active tanks located'at opposed sides of a marine vessel. Active tank 1, for instance, may take the form of an elongate rectangular box some of the sides of which may be regular parts of the structure of the vessel. For example, active tank I may be defined in part by a vertical portion of the outer hull of the vessel and by a false bottom or horizontal floor portion 3 of the vessel. Active tank 1 is further defined by upper horizontal wall 4 and by cooperating vertical walls 5,6, and 7. While the shape of active tank 1 is illustrated as that of a long rectangle box as seen more clearly in FIG. 2, it is to be understood that it may readily take other shapes.

A counterpart to active tank 1 is active tank 1a located on the opposite vertical portion 2a of the outer hull of the vessel, and whose structure is completed by horizontal floor portion 3a, upper horizontal wall 4a, and cooperating vertical walls 5a, 6a, and 7a. The component walls of active tanks 1 and 1a are each assembled so as to be substantially leak-proof.

Wall 5 is supplied with apertures 8 and 9 respectively aligned with corresponding apertures 8a and 9a in the opposite wall 5a. Such alignment permits apertures 8 and 8a to support ram thruster shaft 10, which may be mounted in leak-proof glands (not shown) associated with apertures 8 and 8a, permitting shaft 10 to be freely translated along its axis. Similarly, apertures 9 and 9a support ram thruster shaft 11 for translation along its axis. Shafts l0 and 11, being bound together by the ram cross headers 12 and 12a, are adapted to be moved as an integral system by ram 13.

Motion of shafts l0 and 11 is imparted at their respective ends 14 and 15 to rectangular piston 16, whose position determines the effective volume of active tank 1. Likewise, the position of the respective opposite ends 14a and 15a of shafts l0 and 11 determines the position of piston 16a and thus determines the effective volume of active tank la. It is seen that the apparatus is arranged so that when the effective volume of active tank 1 is maximum, that of active tank la is minimum, and vice versa.

Floor portions 3 and 3a are provided with respective apertures or ports 17 and 17a for transfer of ballast liquid. These latter may be directly joined by a pipe of large rectangular size or other piping or may simply communicate through a channel region or ballast transfer means 18 between the outside bottom 19 of the hull of the vessel and the floor 20 that includes floor portions 3 and 3a.

Although not indicated in FIGS. 1 and 2 for the sake of providing clarity in the drawing, the ballast transfer channel region 18 is filled with a ballast liquid; such material also fills the volume of active tank 1 between wall 2 and piston 16 and the volume of tank 1a between wall 2a and piston 16a. No air or other gas is present within this total region, as it is entirely filled with ballast liquid supplied from a ballast reservoir. Thus, the liquid presents no free surface. No significant pressure head is present against which the ram 13 must work.

Pistons l6 and 16a may be provided with close clearances or other such conventional means for substantially preventing leakage of ballast liquid past, for instance, their respective interfaces with walls 3, 4, 5, 6 and 7 and 3a, 4a, 6a, and 7a. Leakage of ballast liquid past pistons 16 and 16a is further controlled by application of a compressed gas such as air or nitrogen to the backs of pistons 16, 16a. Gas under pressure from a compressor (not shown) is applied by pipe 24 and via pipes 25 and 25a respectively through walls and 5a to the respective regions behind pistons 16 and 16a. The pressure level of the gas may be manually adjusted with respect to maximum pressures to be expected within the ballast liquid, or may be automatically controlled by conventional sensors for measuring such pressures. Should ballast liquid leak past the various described elements for maintaining minimum ballast liquid leakage, conventional pump means (not shown) may be employed for returning such liquid to the system ballast reservoir.

As is seen particularly in FIG, 2 where arrow 37 represents the direction of the fore-aft axis of the vessel, ram 13 is placed centrally betweenactive tanks 1 and la. Ram 13 is a hydraulic actuator of generally conventional type having a piston 26 located in a closed hollow cylinder 27, piston 26 being mounted on an actuator thrust rod 29. Rod 29 extends through glands (not shown) in the opposed ends of cylinder 27 and is free to translate therein. End 28 of thrust rod 29 is fastened centrally in ram cross header 12, while its end 28a is similarly fastened in ram cross header 12a. Piston 26 is driven to the right or to the left according to the sense of flow of hydraulic liquid in pipe 30 with respect to its sense of flow in pipe 30a under control of hydraulic pump 31. Pump 31 may be driven via shaft 33 and coupling 32 from a reversible'electric motor 34, for example. Other well known directionally controllable pump and motor combinations may be substituted for pump 31 and motor 34.

FIGS. 1 and 2 illustrate the two extreme conditions of the apparatus. For example, in FIG. 2, ram 13 has moved pistons 16 and 16a to their extreme left positions, electrical command signals having been applied by electrical leads 35 to motor 34 to cause pump 31 to operate, causing hydraulic liquidflow within pipes 30, 30a as indicated by the respective arrows 36 and 360. In FIG. 2, substantially all ballast liquid has been forced from active tank 1 through channel 18 and then through rectangular port or opening 170 into active tank la, thus providing a desired balancing couple of a first sense to the hull of the vessel.

In the other extreme condition of the control system, as illustrated in FIG. 1, ram 13 has moved pistons 16 and 16a to their extreme right positions, electrical command signals having been applied to motor 34 to reverse the flow of fluid in pipes 30 and 30a. Substantially all ballast liquid is thus forced from active tank la through rectangular aperture or port 17a, channel 18, and rectangular aperture 17 providing a righting couple of a second or reversed sense to'the hull of the ship.

It is thus seen that the embodiment of FIG. 1 consists of a ram 13 operating active tank pistons 16, 16a through a common thrust shaft 29. The enclosed volume behind pistons 16, 16a contains a gas under pressure, while the remainder of the closed system, including active tanks 1 and la and the return athwartship ballast transfer channel 18, contains ballast liquid. Forces applied by ram 13 are determined by control signals derived from measured ship motions. As ram 13 moves in one sense or the other from its null position, a corresponding moment is applied to the hull of the ship because of the consequent assymetric distribution of stabilizing ballast liquid. 7

It is understood that the electrical command signals applied to leads 35 are derived from sensors which derive combinations of inertial measures or terms generally representing the instantaneous roll status of the vessel, particularly including terms which may be used to predict its immediate future status, such as roll acceleration. Such signal combinations and their manner of derivation do not necessarily form a part of the present invention. They need not be described here in detail, since suitable command signal sources appear in the prior art covering active ship 's stabilization system of various types. For example, the command signal source described in US. Pat. No. 2,979,010 to F. D. Braddon, L. F. Beach, and H. J. Chadwick, entitled Ship Stabilization System, issued Apr. 11, 1961 and assigned to the Sperry Rand Corporation may be employed. Reference may be further had, for example, to US. Pat. No. 2,960,959 to J. H. Chadwick and .l. Bentkowsky, entitled Roll Stabilization System for Marine Vessels, issued Nov. 22, 1960, and to US. Pat. No. 3,020,869 to L. F. Beach, entitled Activated Fin Ship Stabilizer, issed Feb. 13, 1962, both patents also being assigned to the Sperry Rand Corporation.

The versatility of the invention is illustrated on one I hand by the fact that it may readily employ the types of command signals found useful, for instance, in the fin or other stabilizer types of system. While the invention is highly effective when used alone during docking maneuvers and at loading stations where a fin type of stabilizer is ineffective, it may also be efficiently used when the vessel is under way. Its operating effectiveness may be augmented when the vessel is under way, especially at thevessel's highest operating speeds, by a tin stabilizer system using the same source of command signals.

The versatility of the invention is further exhibited in an embodiment which makes use of a ballast liquid communication path partially exterior of the hull of the vessel in place of using channel region 18 of FIG. 1. Such an adaptation is shown in FIG. 3, where correspnding reference numerals are used for parts corresponding to parts found in the arrangement of FIGS. 1 and 2. Since such corresponding parts operate in substantially the same manner in FIG. 3 as they operate in FIGS. 1 and 2, they do not require further detailed discussion.

In FIG. 3, it is seen that sections of the hull portions 2 and 2a have been removed respectively adjacent pistons 16 and 16a. Active tanks 1 and la are now in substantially unrestricted open communication with the sea, so that sea water is used as the ballast fluid. For example, hull portion 2 has a port or opening 40 substantially the same size as the face of piston 16 and generally aligned with it. Opening or port 40 is supplied with baffles, such as baffle 41, whose function will be explained. In a similar way, hull portion 2a is provided with a large port 40a substantially the same size as the face of piston 16a and generally aligned with it. Opening or port 40a is supplied with a set of baffles such as baffle 41a.

In operation, sea water is drawn into one of the active tanks -1 and 1a is expelled from the other. FIG. 3, for example, illustrates the apparatus in the condition in which ram 13 has moved pistons 16 and 16a to their extreme right positions. Substantially all ballast liquid has been forced from active tank la through port 40a, being directed downward as indicated by arrow 420 by the baffles 41a. At the same time, ballast liquid has been drawn from the sea into tank 1 through port 40, such flowing in the sense of arrow 42 because of the presence of baffles including baffle 41. Should ram 13 be commanded to move pistons 16, 16a to their extreme leftward position, sea water would be drawn into active tank 1a while being expelled from active tank 1. In both instances, any differential between the amounts of liquid ballast present in active tank 1 and 11: produces a desired righting roll motion of the vessel. Such is further augmented by a cooperating dynamic moment produced by the vertical components of sea water flow directed by baffles 41, 41a during intake and expulsion of ballast liquid. There are no free liquid surfaces present in the active tanks of the embodiment.

In the various embodiments of the invention, the active tanks, no matter what their instantaneous volumes may be, are filled with ballast liquid having no free surface. The transfer of liquid ballast is therefore always under positive and efficient control of the hydraulic ram 13 and the production of stabilizing moments is independent of ships attitude. Acceleration of the ship about its various axes can inject no influence by adversely affecting a free surface of ballast fluid. Further, the substantial pressure head characterizing prior art active tank stabilizer systems is absent and no signifi cant work must be done bythe ram because of the presence of such pressure heads.

FIGS. 9 and 10 illustrate a preferred embodiment of the invention also characterized by complete freedom from free ballast liquid surfaces and their attendant difficulties. Thd active tank stabilizer device is located transversely of the vessel between its -upright hull walls 2, 2a and is preferably placed at a surface 20, such as the false bottom of the vessel lying proximate the actual bottom 19 of the ship's hull. The stabilizer device comprises a liquid filled chamber 200 within which a generally conformal, actively movable float element 201 is located. Float 201 has smoothly curved hydrodynamically strema lined ends 202 and 202a and, being hollow and empty of liquid, may be constructed by well known methods of a low density metal or of reenforced plastic materials. Thus, float 201 reading floats in any liquid placed within chamber 200.

Float 201 is constrained to float in a predetermined manner by a set of four flexible cables 203, 203a, 203b, and 203a. These several cables are similarly arranged at the respective corners of float 201; for example, cable 203b, seen most clearly in FIG. 10, is affixed at an upper end by clamp 204b to a vertical side of float 201. Cable 203b is also fixed at its lower end, as by welding or clamping, within the apex 205b of a vee shaped or conical depression 206b in false floor 20. Cables 203, 2030, and 203d are similarly arranged. For example, it is seen in FIG. 10 that cable 203v is affixed at its upper end by clamp 204c to a vertical wall of float 201, while its other end is secured within depression 2060 at apex 2050. It is thus apparent that float 201 is capable of being moved transverse of the ship, in the sense indicated by arcuate arrows 207, 207a, for displacing ballast liquid located at one end of chamber 200 and for causing it to flow past float 201 to the 0pposite end of chamber 200. It is seen that at any point on the surface of float 201 may move in an arcuate path when chamber 200 is filled with ballast liquid and the float is forced to move by means yet to be described.

Flow of liquid from one end of chamber 200 to the other is facilitated by desirably shaping the end walls 210 and 210a of chamber 200. For example, it has been observed in the foregoing that float 201 is equipped with hydrodynamically smooth curved end walls 202 and 202a. The corresponding end walls 210 and 210a of chamber 200 are shaped in a generally similar manner and particularly so that end wall 202, for instance, may move along an arcuate path toward the generall conformal surface of wall 210, efficiently sweeping ballast liquid out of the volume between walls 202 and 210.

For controlled movement of float 202 within chamber 200 for causing movement of ballast liquid transverse of the ship, a ram rod having portions 10 and 10a is-coupled to the upper side of float 202 by a linkage 212 which may be of well known Rapson slide type. Linkage 212 may be of any known type suitable for transmittingtranslating forces to float 202 while still permitting relatively small vertical movment of float 202. Ram rod portion 10, for example, projects through a stuffing box (not shown) into a conventional hydraulic ram 214, the interior of which may be supplied via pipe 215 with fluid under pressure for moving ram rod 10 and thus causing forces to be exerted via linkage 212 to move float 202 to the right in FIG. 10 about the pivot points of cables 203, 203a, 203b, and 2030. Similarly, ram rod portion 10a projects into hydraulic ram 214a, which may be supplied via pipe 215a with hydraulic fluid under pressure for moving ram rod 10a. Thus, forces applied via linkage 212 move float 202 to the left in the figure. The liquid displaced by motion of float 202 thus causes a righting moment to be exerted relative to the longitudinal axis of the vessel under control of appropriate command signals from inertial references.

While the invention has been described in its preferred embodiments, it is to be understood that the words which have been used are words of description rather than of limitation and that changes within the purview of the appended claims may be made without departure from the true scope and spirit of the invention in its broader aspects.

I claim:

l. in a stabilizer for correcting dynamic roll conditions in a marine vessel having hull means:

active stabilizer tank means having an interior, movable wall means for varying the volume of said interior, actuator means responsive to said dynamic roll conditions for controlling the position while said interior of said movable wall means, and liquid ballast transfer means permitting controlled flow of liquid ballast means through said transfer means upon movement of said movable wall means, said liquid ballast means substantially filling said variable volume and said liquid transfer means for the purpose of substantially preventing the formation of any free liquid surface of said liquid ballast means within said variable volume or said liquid transfer means, said active stabilizer tank means comprising first and second active stabilizer tank means adapted to be located at opposite sides of said hull means within said marine vessel and having first and second respective interior volumes, said movable wall means comprising first and second wall means each respectively having first and second surface means,

said actuator means comprising common actuator means for positioning said first and second movable wall means within said respective first and second active stabilizer tank means for defining respective first and second variable volumes,

said liquid ballast means filling said first and second means. 

1. In a stabilizer for correcting dynamic roll conditions in a marine vessel having hull means: active stabilizer tank means having an interior, movable wall means for varying the volume of said interior, actuator means responsive to said dynamic roll conditions for controlling the position while said interior of said movable wall means, and liquid ballast transfer means permitting controlled flow of liquid ballast means through said transfer means upon movement of said movable wall means, said liquid ballast means substantially filling said variable volume and said liquid transfer means for the purpose of substantially preventing the formation of any free liquid surface of said liquid ballast means within said variable volume or said liquid transfer means, said active stabilizer tank means comprising first and second active stabilizer tank means adapted to be located at opposite sides of said hull means within said marine vessel and having first and second respective interior volumes, said movable wall means comprising first and second wall means each respectively having first and second surface means, said actuator means comprising common actuator means for positioning said first and second movable wall means within said respective first and second active stabilizer tank means for defining respective first and second variable volumes, said liquid ballast means filling said first and second respective variable volumes and said liquid transfer means, said first and second active stabilizer tank means having respective first and second opposed walls with respective aligned first and second bearing apertures, said movable wall means comprising a first and second piston means operating within said respective first and second stabilizer tank means, and said actuator means comprising: ram meAns and ram thruster shaft means translatable by said ram means, said ram thruster shaft means passing in translatable relation through said first and second bearing apertures for moving said piston means. 